Disorders of purine metabolism in man occur in 5 percent of the population and may lead eventually to clinical disease in 1 percent. The clinical manifestations of these disorders range from gout to severe combined immunodeficiency disease. Although extrapolation of basic concepts derived from a study of model systems in lower organisms has been remarkably successful with regard to the regulation of purine metabolism, until the last few years little has been known about the actual mechanisms of control of this pathway in man. In the present investigation, the regulation of purine metabolism in human cells will be examined by a) a detailed study of the structural properties of several crucial enzymes of purine metabolism, hypoxanthine guanine phosphoribosyltransferase (HPRT), adenine phosphoribosyltransferase (APRT) and adenosine deaminase (ADA), isolated from human cells, b) an evaluation of mechanisms involved in controlling the rate of synthesis and degradation of these enzymes, and c) investigation of the specific nature and consequence of spontaneous and induced mutations involving these three enzymes in the pathway. During the tenure of this grant specific methods of procedure will include immunoadsorbent chromatography, enzyme immunoprecipitation, molecular hybridization, and somatic cell hybridization. Results based on these studies in vitro and in cell culture will be integrated, when possible, with information derived from clinical studies in vivo. It is hoped that this broad but goal-directed approach will help not only to define the pathogenesis of aberrant control mechanisms in man but also that information of direct therapeutic relevance may emerge.